# Pipe size chart (DN to inch)

DN15 to DN300: the inch equivalent, outside diameter, common wall, weight per metre and external area for insulation take-off.

- Page: https://jianzhujisuan.com/en/pipe-dn-table
- Data checked: 2026-10-25

## Table

| DN | Inch | Outside dia (mm) | Wall (mm) | Weight (kg/m) | Area (m²/m) |
|---|---|---|---|---|---|
| DN15 | 1/2" | 21.3 | 2.8 | 1.28 | 0.067 |
| DN20 | 3/4" | 26.9 | 2.8 | 1.66 | 0.085 |
| DN25 | 1" | 33.7 | 3.2 | 2.41 | 0.106 |
| DN32 | 1¼" | 42.4 | 3.5 | 3.36 | 0.133 |
| DN40 | 1½" | 48.3 | 3.5 | 3.87 | 0.152 |
| DN50 | 2" | 60.3 | 3.8 | 5.29 | 0.189 |
| DN65 | 2½" | 76.1 | 4.0 | 7.11 | 0.239 |
| DN80 | 3" | 88.9 | 4.0 | 8.37 | 0.279 |
| DN100 | 4" | 114.3 | 4.0 | 10.88 | 0.359 |
| DN125 | 5" | 139.7 | 4.0 | 13.39 | 0.439 |
| DN150 | 6" | 168.3 | 4.5 | 18.18 | 0.529 |
| DN200 | 8" | 219.1 | 6.0 | 31.53 | 0.688 |
| DN250 | 10" | 273.0 | 6.5 | 42.72 | 0.858 |
| DN300 | 12" | 323.9 | 7.9 | 61.56 | 1.018 |

## How to use

- A drawing calling DN50 means a 2 inch pipe, 60.3 mm outside diameter, with 2 inch flanges and valves.
- For insulation, multiply the external area by thickness and insulation density.
- For supports, look up the maximum spacing for that diameter — 6 m is typical above DN100.

## Common mistakes

- Treating DN as the outside diameter — DN50 is 60.3 mm outside, and a 10 mm error will not fit.
- Reading DN as a decimal inch — 1 inch is 25.4 mm, but 1 inch pipe is 33.7 mm outside because DN is sized on the bore series.
- Using plain steel wall thickness for galvanised pipe — the zinc adds 3-5% to the weight.

## Questions

### What is DN50 in inches?

Two inch, 60.3 mm outside diameter, commonly 3.8 mm wall, 5.29 kg per metre.

### What is the outside diameter of DN25?

33.7 mm, which is 1 inch. Note the outside diameter is 8.7 mm larger than the DN, so fittings are selected on outside diameter.

### What is the difference between DN, De and Φ?

DN is a nominal size close to the bore but not exact; De is the outside diameter of plastic pipe; Φ usually means outside diameter × wall thickness. They are not interchangeable.

## Related calculators

- [Steel Pipe Weight Calculator](https://jianzhujisuan.com/en/steel-pipe-weight): Mass per metre, per length and in total from OD and wall thickness.
- [Pipe Support Calculator](https://jianzhujisuan.com/en/pipe-support): Run length and spacing give bracket count and steel weight.
- [Insulation Thickness Calculator](https://jianzhujisuan.com/en/insulation-thickness): Insulation thickness from a target U-value.